Photoaddressable side group polymers of high sensitivity

ABSTRACT

The invention provides an optical method which permits, with the aid of 6 simple measurements, a conclusion regarding the suitability of antennas (groups which can absorb electromagnetic radiation) for incorporation into photoaddressable polymers.

The invention relates to photoaddressable side group polymers in which ahigh birefringence can be induced by irradiation, so that they aresuitable for the production of components for storage of opticallyavailable information or as optically switchable components.

Photoaddressable side group polymers which have been recommended arespecial branched polymers: side groups of different types, of which onetype (called "A") can absorb electromagnetic radiation and another type(called "M") is a mesogenic group anisotropic in shape, are positionedon a linear backbone, connected via molecular parts which act asspacers.

So that the interaction of the mesogenic groups is not impeded, in thepast the mesogenic groups have usually been coupled to the spacing groupvia an oxygen atom, because it has been assumed to date thathigher-valency atoms with their substituents in this position impede theinteraction and therefore the photoaddressability because of theirsteric requirement.

The mechanism of photoaddressed orientation is probably based on thepossibility of achieving an orientation of the mesogenic groups andtherefore a change in the state of order by electromagnetic radiation.However, the photoaddressable polymers known to date still have thedisadvantage that the changes in the state of order which can beproduced are too small, the change in the state of order takes place tooslowly and/or the patterns written in slowly fade again during storage.

The object of the invention was therefore to provide polymers which donot have these disadvantages or have them to a lesser extent.

Surprisingly, a connection has now been found between the experimentallydeterminable interaction of the group A, which can absorbelectromagnetic radiation, with respect to a standard and the quality ofthe photoaddressability of the polymer. This finding allows thesuitability of the groups A to be tested before their incorporation intothe polymer.

The invention thus relates to polymers which have a main chain whichacts as a backbone and, branching therefrom, covalently bonded sidegroups of the formulae

    --S.sup.1 --T.sup.1 --Q.sup.1 --A                          (I) and

    --S.sup.2 --T.sup.2 --Q.sup.2 --M                          (II)

wherein

S¹ and S² denote the atoms O or S or the radical NR⁰,

R⁰ denotes hydrogen or C₁ -C₄ -alkyl,

T¹ and T² denote the radical (CH₂)_(n), which can optionally beinterrupted by --O--, --NR⁰ -- or --OSiR⁰ ₂ O-- and/or can optionally besubstituted by methyl or ethyl,

Q¹ and Q² denote a direct bond, --O--, --COO--, --OCO--, --CONR⁰ --,--NR⁰ CO-- or --NR⁰ --, or

S¹ T¹ Q¹ or S² T² Q² denotes a bivalent group of the formula ##STR1##

A denotes a unit which can absorb electromagnetic radiation,

M denotes a mesogenic unit anisotropic in shape and

n denotes an integer from 2 to 12,

characterized in that A has an extinction modulus ΔΔE of greater than0.2 (measured as described below).

For the purposes of the invention, the value ΔΔE is measured on acompound of the formula H--Q¹ --A or HS¹ T¹ Q¹ A wherein Q¹, S¹, T¹ andA have the abovementioned meaning and H represents the hydrogen radical.

The extinction modulus ΔΔE is determined from the changes in extinctionΔE of the longwave flank of the absorption band of 3 solutions of thefollowing substances, that is to say

Solution A H--Q¹ --A or HS¹ T¹ Q¹ A is dissolved in the lowest possibleconcentration in a solvent which has the lowest possible polarity. Theconcentration is preferably chosen here such that the steepest possibleedge results when the absorption is measured. In the case of dyestuffs,which as a rule have a high molar extinction, this concentration ispreferably 10⁻³ molar.

Solution B The standard is dissolved in the same solvent in the highestpossible concentration, preferably 1 molar, and the absorption edge isrecorded.

Solution C This solution comprises H--Q¹ --A or HS¹ T¹ Q¹ A and thestandard in the concentrations of solutions A and B.

3 absorption edges are thus obtained: that of the standard, which ingeneral is at a short wavelength, and the absorption edge of solution Aand the edge of solution C, which is shifted parallel to this to a longwavelength.

On the longest-wavelength edge, that is to say of solution C, thewavelength belonging to the extinction 0.8 defines the referencewavelength λ. The extinction values E of the three solutions A, B and Care now in each case read off at the wavelengths λ and λ+50, where

    E.sub.solution C >E.sub.solution A >E.sub.solution B.

To determine the value of ΔE, the following differences are obtained forthe wavelengths λ and λ+50:

    ΔE.sub.A =E (λ).sub.solution A -E (λ+50).sub.solution A

    ΔE.sub.B =E (λ).sub.solution B -E (λ+50).sub.solution B

    ΔE.sub.C =E (λ).sub.solution C -E (λ+50).sub.solution C

From these three differences, the increase in extinction of the dyestuffdue to the presence of the standard is obtained as the difference ΔΔE:

    ΔΔE=ΔE.sub.C -(ΔE.sub.B +ΔE.sub.A)

The standard should be as polar and/or polarizable as possible. Thepolarity of the solvent should be as low as possible.

In a preferred form, 1,3-dinitrobenzene is used as the standard anddioxane is used as the solvent.

As explained above, A should be able to absorb electromagneticradiation. The absorption maxima (λ_(max)) of preferred groups A can bein the near IR, in the range of visible light or in the UV, preferablyin the wavelength range of 320-1500 nm, in particular 350 to 800 nm.Where the terms "chromophore" or "dyestuff" are used in the context ofthis invention, they are not limited to the wavelength range of visiblelight, but are based on the groups A.

Groups A, which give ΔΔE values above 0.2, can be chosen from theradicals of the following classes of dyestuffs (cf. for example, G.Ebner and D. Schulz, Textilfarberei und Farbstoffe [Textile Dyeing andDyestuffs], Springer-Verlag, Berlin Heidelberg 1989):

I. Azo dyestuffs

1. Monoazo dyestuffs, such as, for example

C.I. Mordant Yellow 1

C.I. Mordant Blue 78

C.I. Disperse Blue 79

C.I. Disperse Yellow 5

2. Disazo dyestuffs, such as, for example,

C.I. Mordant Yellow 16

C.I. Disperse Yellow 23

C.I. Basic Brown 1

C.I. Disperse Yellow 7

II. Quinonoid dyestuff

1. Quinonoid disperse and mordant dyestuffs such as, for example,

C.I. Disperse Orange 11

C.I. Disperse Blue 5

C.I. Disperse Blue 7

C.I. Mordant Violet 26

C.I. Mordant Blue 23

III. Metal complex dyestuffs

C.I. Ingrain Blue 14

IV. Meroquinonoide dyestuffs

1. Diphenylmethane dyestuffs, such as, for example,

Basic Yellow 3

2. Triphenylmethane dyestuffs, such as, for example,

C.I. Basic Violet 3

C.I. Basic Green 4

C.I. Mordant Blue 1

C.I. Mordant Blue 28

3. Quinoneimine dyestuffs, such as, for example,

C.I. Solvent Blue 22

4. Acridine dyestuffs, such as, for example,

Acridine Orange 2 G

5. Thioxanthene dyestuffs; such as, for example,

Pyronin G, C.I. 45005

6. Phenazine dyestuffs, such as, for example,

C.I. Solvent Blue 7

7. Phenoxazine dyestuffs, such as, for example,

C.I. Mordant Blue 10

8. Phenothiazine dyestuffs, such as, for example,

C.I. Mordant Blue 51

9. Squaric acid dyestuffs, such as, for example, those known from EP-A 0145 401

V. Polymethine dyestuffs comprising cationo, aniono and mero(═neutro)cyanines and hemicyanines, such as, for example,

C.I. Disperse Yellow 31

C.I. Disperse Blue 354

C.I. Disperse Red 196

C.I. Disperse Yellow 99

VI. Nitro and nitroso dyestuffs, such as, for example,

C.I. Disperse Yellow 42

C.I. Disperse Yellow 1

VII. Heterocyclic dyestuffs

1. Perinones, such as, for example,

C.I. Disperse Yellow 58

2. Naphthalimides, such as, for example,

Disperse Yellow 11

3. Quinophthalone, such as, for example,

Disperse Yellow 54, Disperse Yellow 64

4. Coumarins, such as, for example, those known from DE 15 94 845, 16 70999, 20 65 076

5. Pyrazolines, such as, for example, those known from DE 11 55 418, 1445 705, 14 19 329

6. Stilbene dyestuffs, such as, for example,

C.I. Fluorescent Brightener 30

C.I. Fluorescent Brightener 46

In particular, the groups A can be chosen from the monovalent radicalsof the following compounds:

    Het.sup.1 (═Z).sub.n ═Het.sup.2                    (I)

wherein

Het¹ denotes ##STR2##

Z denotes CH--CH or N--N,

n denotes zero or 1,

Het² denotes ##STR3##

R¹ denotes C₁ -C₆ -alkyl, C₂ -C₆ -alkenyl, C₅ -C₁₀ -cycloalkyl or C₇-C₁₅ -aralkyl,

R² denotes C₁ -C₆ -alkyl, C₁ -C₄ -alkoxy, C₆ -C₁₂ -aryl, C₆ -C₁₂-aryloxy, C₁ -C₆ -alkylthio, C₆ -C₁₂ -arylthio, mono- or di-C₁ -C₄-alkylamino, C₆ -C₁₂ -arylamino, C₁ -C₄ -alkyl-C₆ -C₁₂ -arylamino orchlorine,

R³ denotes C₁ -C₆ -alkyl, C₂ -C₆ -alkenyl, C₅ -C₁₀ -cycloalkyl, C₆ -C₁₂-aryl, C₇ -C₁₅ -aralkyl,

R⁴ denotes C₁ -C₆ -alkyl, C₆ -C₁₂ -aryl, CN, COOR³, CO--R³,

X denotes O, S, Se, NR¹, CR⁸ ₂,

R⁸ denotes C₁ -C₆ -alkyl,

the asterisks characterize the position of the exocyclic C═C double bondand the curved lines in the structures (5) and (6) denote hydrogen or--CH═CH--CH═CH--;

    Het.sup.1 (═Z).sub.n ═Het.sup.3                    (II)

wherein ##STR4##

R⁵ denotes hydrogen, C₁ -C₆ -alkyl, C₁ -C₆ -alkoxy, fluorine orchlorine,

R⁶ denotes hydrogen, C₁ -C₆ -alkyl, C₁ -C₆ -alkoxy, fluorine, chlorine,CN, NO₂, NHCOR³ or NHSO₂ R³,

Y denotes oxygen, C(CN)₂, C(CN)COOR³ or ##STR5##

Het¹, Z, n, the asterisk and R³ have the meaning given above under (I)and

R³ independently of R³ represents the meaning given above under R³ ;##STR6## wherein

Y has the meaning given above under (II)--with the exception ofoxygen--and additionally denotes ##STR7##

X, R¹, R³, R⁴ and the asterisk have the meaning given above under (I)and

R⁷ denotes hydrogen, C₁ -C₆ -alkyl, C₁ -C₆ -alkoxy, COOR³, chlorine, NO₂or CN; ##STR8## wherein

R³ and R^(3') independently of one another have the meaning given abovefor R³ under (I),

R⁵ and R⁶ have the meaning given above under (II) and

Y has the meaning given above under (III),

R⁹ denotes hydrogen, C₁ -C₆ -alkyl, C₆ -C₁₂ -aryl, CN or COOR³ andfurthermore additionally

R^(3') denotes hydrogen, ##STR9## and

R^(3') and R⁵ together denote --(CH₂)₂ --, --(CH₂)₃ --, --C(CH₃)₂ --CH₂--CH(CH₃)-- or --OCH₂ CH₂ --; ##STR10## wherein

Het⁴ denotes ##STR11##

R¹⁰ denotes CN, NO₂ or COOR³,

R¹¹ denotes C₁ -C₆ -alkyl, C₁ -C₆ -alkoxy, chlorine, amino, C₁ -C₇-acylamino or di-C₁ -C₄ -alkylamino,

R¹² denotes C₁ -C₆ -alkyl, C₅ -C₁₂ -aryl, CN or COOR³,

R¹³ denotes hydrogen, CN or NO₂ and R¹, R², R⁷, R³, R^(3'), R⁵ and R⁶have the meaning given in the case of (I), (III) and (IV); ##STR12##wherein

X¹ denotes hydrogen, hydroxyl, mercapto, CF₃, CCl₃, CBr₃, halogen,cyano, nitro, COOR¹⁹, C₁ -C₆ -alkyl, C₅ -C₁₂ -cycloalkyl, C₁ -C₁₂-alkoxy, C₁ -C₁₂ -alkylthio, C₆ -C₁₂ -aryl, C₆ -C₁₂ -aryloxy, C₆ -C₁₂-arylthio, C₁ -C₆ -alkylsulphonyl, C₆ -C₁₂ -arylsulphonyl,aminosulphonyl, C₁ -C₆ -alkylaminosulphonyl, phenylaminosulphonyl,aminocarbonyl, C₁ -C₆ -alkylaminocarbonyl, phenylaminocarbonyl, NR¹⁹,R²⁰, NH--CO--R¹⁹, NH--SO₂ -R¹⁹, NH--CO--NR¹⁹ R²⁰, NH--CO--O--R¹⁹ or SO₂--CF₃, wherein R¹⁹ and R²⁰ independently of one another representhydrogen, C₁ -C₄ -alkyl or phenyl,

wherein one of the radicals R¹ to R¹³ (including R^(3')), in particularone of the radicals R¹ and R³, represents a single bond which allowslinkage to the group Q¹, Q¹ then representing a single bond in the caseof the radicals R¹, R³ and R^(3').

Particularly preferred compounds (V) correspond to the formulae##STR13##

wherein Het⁴ represents one of the structures 26 to 33, and ##STR14##

wherein Het⁴ represents one of the structures 26, 27, 30, 32 or 34 to39.

As described above, the group A is bonded to the main chains of thepolymers according to the invention via the intermediate members Q¹, T¹and S¹. The dyestuffs mentioned above can already contain theseintermediate members in their entirety or in part; cf the legend to thesubstituents. Dyestuff radicals which are suitable as A are therefore tobe understood as the dyestuffs shortened in each case by suchintermediate members already contained in the product. On the otherhand, if the dyestuffs do not contain the intermediate members Q¹, T¹and S¹ or contain them only in part, they can be converted byappropriate reaction into the desired reactive derivatives, which arethen suitable for building up the polymers according to the invention.

The unit --Q¹ --T¹ --S¹ -- can thus represent, for example, --NR⁰--(CH₂)_(n) --O--. For a given group A, suitable compounds of thestructure A--NR⁰ --(CH₂)_(n) --OH can be provided for introduction of Ainto the polymers according to the invention or into the monomers to bepolymerized. (Analogous statements apply for another meaning of Q¹, T¹and S¹). Such suitable compounds can thus include, for example, thefollowing compounds: ##STR15##

Additionally to the above definitions, one of the substituents R¹ to R¹³(including R^(3')), in particular one of the radicals R¹ and R³, perradical A denotes a single bond which allows linkage to the group Q¹.

The compounds

(1) A--Q¹ --T¹ --S¹ --H

(2) A--Q¹ --T¹ --S¹ --OC--CH═CH₂

(3) A--Q¹ --T¹ --S¹ --OC--C(CH₃)═CH₂

(4) A--Q¹ --T¹ --S¹ --(CH₂)_(n) --OH

(5) A--Q¹ --T¹ --S¹ --CH₂ --CHOH--CH₃

(6) A--Q¹ --T¹ --S¹ --CH₂ --C(CH₃)₂ --CH₂ --OH

wherein A, Q¹, T¹ and S¹ have the abovementioned meanings and nrepresents an integer from 2 to 12, and the acrylates and methacrylatesof the compounds 4 to 6 are, to our knowledge, new and this inventiontherefore also relates to them. The compounds can be prepared byprocesses analogous to those for similar compounds.

The polymers according to the invention contain no groups A of theformula ##STR16## wherein

R¹⁴ to R¹⁶ independently of one another denote C₁ -C₆ -alkyl, hydroxyl,C₁ -C₆ -alkoxy, phenoxy, C₁ -C₆ -alkythio, phenylthio, halogen, CF₃,CCl₃, CBr₃, nitro, cyano, C₁ -C₆ -alkylsulphonyl, phenylsulphonyl,COOR¹, aminosulphonyl, C₁ -C₆ -alkylaminosulphonyl,phenylaminosulphonyl, aminocarbonyl, C₁ -C₆ -alkylaminocarbonyl orphenylaminocarbonyl,

R¹⁷ denotes halogen, C₁ -C₆ -alkyl, hydroxyl, C₁ -C₆ -alkoxy, phenoxy,C₁ -C₄ -acylamino or C₁ -C₄ -alkylsulphonylamino,

R¹⁸ denotes halogen, C₁ -C₆ -alkyl, hydroxyl, C₁ -C₆ -alkoxy or phenoxyand

X¹ denotes hydrogen, hydroxyl, mercapto, CF₃, CCl₃, CBr₃, halogen,cyano, nitro, COOR¹⁹, C₁ -C₆ -alkyl, C₅ -C₁₂ -cycloalkyl, C₁ -C₁₂-alkoxy, C₁ -C₁₂ -alkylthio, C₆ -C₁₂ -aryl, C₆ -C₁₂ -aryloxy, C₆ -C₁₂-arylthio, C₁ -C₆ -alkylsulphonyl, C₆ -C₁₂ -arylsulphonyl,aminosulphonyl, C₁ -C₆ -alkylaminosulphonyl, phenylaminosulphonyl,aminocarbonyl, C₁ -C₆ -alkylaminocarbonyl, phenylaminocarbonyl, NR¹⁹R²⁰, NH--CO--R¹⁹, NH--SO₂ --R¹⁹, NH--CO--NR¹⁹ R²⁰, NH--CO--O--R¹⁹ or SO₂--CF3, wherein R¹⁹ and R²⁰ independently of one another representhydrogen, C₁ -C₄ -alkyl or phenyl.

Preferred mesogenic units M correspond to the formula ##STR17## wherein

R²¹ to R²⁵ independently of one another denote hydrogen, halogen, C₁ -C₄-alkyl, C₁ -C₄ -alkoxy, CF₃, nitro, SO₂ CH₃, SO₂ NH₂ or cyano, whereinat least one of the substituents R²¹ to R²⁵ must be other than hydrogen,

Y denotes a direct bond, --COO--, --OCO--, --CONH--, --NHCO--, --O--,--NH--, --N(CH₃)-- or --N═N-- and

X² denotes hydrogen, hydroxyl, mercapto, CF₃, CCl₃, CBr₃, halogen,cyano, nitro, COOR¹⁹, C₁ -C₆ -alkyl, C₅ -C₁₂ -cycloalkyl, C₁ -C₁₂-alkoxy, C₁ -C₁₂ -alkylthio, C₆ -C₁₂ -aryl, C₆ -C₁₂ -aryloxy, C₆ -C₁₂-arylthio, C₁ -C₆ -alkylsulphonyl, C₆ -C₁₂ -arylsulphonyl,aminosulphonyl, C₁ -C₆ -alkylaminosulphonyl, phenylaminosulphonyl,aminocarbonyl, C₁ -C₆ -alkylaminocarbonyl, phenylaminocarbonyl, NR¹⁹R²⁰, NH--CO--R¹⁹, NH--SO₂ --R¹⁹, NH--CO--NR¹⁹ R²⁰, NH--CO--O--R¹² or SO₂--CF₃, wherein R¹⁹ and R²⁰ independently of one another representhydrogen, C₁ -C₄ -alkyl or phenyl,

but wherein

R²¹ to R²⁵ all represent hydrogen when A corresponds to a radical of theformula (VI).

The preferred polymers according to the invention contain solelyrepeating units with the side groups I and II, and in particularpreferably those of the formulae ##STR18## where R═H or methyl.

Preferred examples of the groups T¹ and T² are, independently of oneanother, ##STR19## wherein

n is an integer from 2 to 6 and

m and o independently of one another are integers from 0 to 2, the totalof which is at least 1.

S¹ T¹ Q¹ or S² T² Q² is also preferably ##STR20##

Possible preferred side groups II are, in particular, those of theformula ##STR21## wherein

X², T², Q² and R²¹ to R²⁵ have the abovementioned meanings.

Preferred monomers for introduction of the side groups II correspond tothe formula ##STR22## wherein

n is an integer from 2 to 6,

R²¹ and R²⁵ independently of one another represent H, F, Cl, Br, OH,OCH₃, CH₃, CF₃, NO₂ or CN and

at least one of the substituents R²¹ and R²⁵ must be other than H, and

X² denotes H, F, Cl, Br, CN, NO₂, COOR¹⁹, C₅ -C₁₂ -cycloalkyl, C₁ -C₁₂-alkoxy or C₆ -C₁₂ -aryl and

R¹⁹, R²¹ and R²⁵ have the abovementioned meaning.

Examples of such monomers are ##STR23##

The main chain of the side group polymers is preferably formed bymonomers which carry the side groups (I), by monomers which carry theside group (II) and, if appropriate, by further monomers, the proportionof monomers which contain the side group (I) being, in particular, 25 to80 mol %, preferably 30 to 70 mol %, the proportion of monomers whichcontain the side group (II) being 20 to 75 mol %, preferably 30 to 70mol %, and the proportion of the further monomers being 0 to 50 mol %,in each case based on the total of all the monomer units incorporated.

Possible "further" repeating units are all structural units which can beincorporated chemically into the side group polymer. They essentiallyserve merely to reduce the concentration of side groups I and II in thepolymer and thus cause virtually a "dilution" effect. In the case ofpoly(meth)acrylates, the "further" monomers comprise ethylenicallyunsaturated copolymerizable monomers, which preferably carryα-substituted vinyl groups or β-substituted allyl groups, preferablystyrene; and also, for example, styrenes which are chlorinated andalkylated or alkenylated on the nucleus, it being possible for the alkylgroups to contain 1 to 4 carbon atoms, such as, for example,vinyl-toluene, divinylbenzene, α-methylstyrene, tert-butylstyrenes andchlorostyrenes; vinyl esters of carboxylic acids having 2 to 6 carbonatoms, preferably vinyl acetate; vinylpyridine, vinylnaphthalene,vinylcyclohexane, acrylic acid and methacrylic acid and/or their esters(preferably vinyl, allyl and methallyl esters) having 1 to 4 carbonatoms in the alcohol component, their amides and nitriles, maleicanhydride, maleic acid half-esters and diesters having 1 to 4 carbonatoms in the alcohol component and half-amides and diamides, and cyclicimides, such as N-methylmaleimide or N-cyclohexylmaleimide; and allylcompounds, such as allylbenzene and allyl esters, such as allyl acetate,diallyl phthalate, diallyl isophthalate, diallyl fumarate, allylcarbonates, diallyl carbonates, triallyl phosphate and triallylcyanurate.

Preferred "further" monomers correspond to the formula ##STR24## wherein

R²⁶ represents an optionally branched C₁ -C₆ -alkyl radical or a radicalcontaining at least one further acrylic radical.

The polymers according to the invention can also contain more than oneside group which falls under the definition of (I), or more than oneside group which falls under the definition of (II), or several sidegroups of the definition both of (I) and of (II), and of these one sidegroup of the definition (I) can also correspond to the formula XIII. Ifside chains of the structure (I) and (II) are present, at least onegroup Q¹ or Q² advantageously has the meaning --O--C₆ H₄ --COO-- or--O--C₆ H₄ --CONR¹⁹.

The polymers according to the invention preferably have glass transitiontemperatures Tg of at least 40° C. The glass transition temperature canbe determined, for example, by the method of B. Volhmer, Grundriβ derMakromolekularen Chemie [Principles of Macromolecular Chemistry], pages406-410, Springer-Verlag, Heidelberg 1962.

The polymers according to the invention in general have a molecularweight, determined as the weight average, of 5,000 to 2,000,000,preferably 8,000 to 1,500,000, determined by gel permeationchromatography (calibrated with polystyrene).

The structural elements of high shape anisotropy and high anisotropy ofthe molecular polarizability are the prerequisite for high values ofoptical anisotropy. The intermolecular interactions of the structuralelements (I) and (II) are established by the structure of the polymerssuch that the formation of liquid crystal states of order is suppressedand optically isotropic, transparent non-scattering films can beproduced. On the other hand, the intermolecular interactions arenevertheless strong enough to cause a photochemically induced,cooperative, directed reorientation process of the photochromic andnon-photochromic side groups on irradiation with polarized light.

Interaction forces which are sufficient for the photoinduced change inconfiguration of the side group (I) to cause a reorientation of the sidegroup (II) in the same direction--so-called cooperativereorientation--preferably occur between the side groups (I) and (II).

In the optically isotropic amorphous photochromic polymers, extremelyhigh values of the optical anisotropy can be induced (Δn=0.01 to 0.2,preferably 0.01 to 0.1). The values are comparable to those which havebeen obtained in monodomains of liquid crystal polymers, or are evengreater than these. They are significantly greater in comparison withamorphous polymers without these structural elements.

States of order are generated and modified in the side group polymers,and their optical properties are thus modulated, by the influence ofactinic light.

Linearly polarized light, the wavelength of which is in the range of theabsorption band of the side groups (I) whose configuration can be variedby photoinduction is preferably used as the light.

The preparation of the side group monomers and their polymerization canbe carried out by processes known from the literature (for example DD276 297, DE 3 808 430, Makromolekulare Chemie [Macromolecular Chemistry]187, 1327-1334 (1984), SU 887 574, Europ. Polym. 18 561 (1982) and Liq.Cryst. 2, 195 (1987)).

Isotropic films can be produced without the need for expensiveorientation processes utilizing external fields and/or surface effects.They can be applied to substrates by spin coating, dipping, casting orother coating processes which are easy to control technologically, canbe introduced between two transparent sheets by pressing or flowing in,or can simply be prepared as a self-supporting film by casting orextrusion. Such films can also be produced from liquid crystal polymerswhich contain the structural elements in the context described by suddencooling, that is to say by a cooling rate of >100 K/minute, or by rapidstripping of the solvent.

The layer thickness is preferably between 0.1 μm and 1 mm, in particularbetween 0.5 and 100 μm.

The photoinduced orientation of the side groups or the writing ofinformation is effected by irradiation with actinic light suitable forthe group A whose configuration can be varied by photoinduction. Thisleads to an angle-dependent photoselection, which causes reorientationof the photochromic groups and--by a cooperative effect--a continuousreorientation of the permanently shape-anisotropic side groups M in thesame direction up to the maximum of perpendicular with respect to theelectrical vector of the stimulating light.

The exposure to light can take place over the whole surface or locallywith linearly polarized, coherent or non-coherent, monochromatic light,the wavelength of which is in the absorption range of the side groups Awhose configuration can be varied by photoinduction.

The information can be written in point form with a laser or inunstructured form over the whole surface with a laser or a lamp or usinga mask or by writing in a holographic refractive index grid at anintensity of 1 to 500 mW/cm² over a period of between 1 and 30,000seconds.

The reorientation process is exceptionally effective. The change inbirefringence Δn which can be achieved below Tg is preferably 0.01 to0.20, in particular 0.05 to 0.10.

The high values of the photochemically induced birefringence and of thephotochemically induced dichroism result from the molecular structure ofthe side groups and the cooperative mechanism of the photoinducedorientation to a state of the same macroscopic orientation of thephotochromic and non-photochromic but permanently shape-anisotropic sidegroups.

The preferred orientation can be chosen as desired, and depends solelyon the choice of the direction of the electrical vector of thestimulating light with reference to the polymer substance. The extent ofthe orientation at a constant temperature and wavelength depends solelyon the irradiated energy, which can be varied either via the time or,within certain limits, via the output of the light source. Theorientation, the birefringence and the dichroism are thus parameterswhich can be chosen as desired and can be reproduced exactly underconstant framework conditions during repeated writing and deletion.

A reproducible, defined, continuously variable birefingence of long-termstability can be produced in the side chain polymers. It can be shown asa defined contrast in transmission in the polarized light. If polymerswith side groups with dichroic properties are used, a dichroism of theabsorption or of the emission can correspondingly be producedreproducibly and in a defined and continuously variable manner. Auniform orientation is produced in the entire polymer film by uniformirradiation conditions. If the irradiation conditions, such as energydose and polarization direction, vary locally, a film which isstructured in respect of the preferred orientation of the side groups isproduced, which leads to pixels of different optical anisotropy.

The preferred direction in the orientation distribution of the opticallyanisotropic film can be reversed again by exposure to non-polarizedactinic light, and the optical isotropy along the perpendicular to thesurface can be reestablished. Renewed irradiation with the same sourcebut a changed position of the electrical vector with reference to thepolymer film leads to a modification of the direction and magnitude ofoptical anisotropy. The system can in this way be switched repeatedlybetween two different states with respect to the direction and magnitudeof the optical anisotropy.

On the basis of these effects, a medium for reversible, optical datastorage is in principle available with the polymers described. As withthe production of the films, all measures for reestablishing themonodomain are dispensed with even after deletion of the information.

The polymers can be used for digital or analog data storage in thebroadest sense, for example for optical signal processing, for Fouriertransformation and folding or in coherent optical correlationtechniques. The lateral resolution is limited by the wavelength of thereading light. It allows a pixel size of 1 to 100 μm.

This property makes the polymers particularly suitable for processingimages and for information processing by means of holograms,reproduction of which can be effected by illuminating with a referencebeam. The interference pattern of two monochromatic coherent lightsources with a constant phase relationship can be stored analogously anda higher storage density can be produced in the storage medium owing tothe relationship between the electrical vector of the light and theassociated preferred direction. Three-dimensional holographic images cancorrespondingly be stored. Read-out is achieved by illuminating thehologram with monochromatic, coherent light. In the case of analogstorage, grey scale values can be established continuously and withlocal resolution. Read-out of information stored in analog form iseffected in polarized light, it being possible to bring out the positiveor negative image, depending on the position of the polarizers. In thiscase, on the one hand the contrast of the film produced by the phaseshift of the ordinary and extraordinary beam can be utilized between twopolarizers, the planes of the polarizer advantageously forming an angleof 45° to the plane of polarization of the writingin light and the planeof polarization of the analyser being either perpendicular or parallelto that of the polarizer. Another possibility is detection of thedeflection angle of the reading light caused by induced birefringence.

The polymers can be used as optical components which can be passively oroptically switchable. Thus, the high photoinduced optical anisotropy canbe utilized for modulation of the intensity and/or of the state ofpolarization of light. Components which have imaging propertiescomparable to lenses or gratings can correspondingly be produced from apolymer film by holographic structuring. The polymers can furthermore beemployed for the production of polarizers.

The invention thus also relates to the use of the polymers described foroptical components. Polarizers are also to be regarded as such opticalcomponents.

The polymers according to the invention can be prepared in the customarymanner by free radical copolymerization of the monomers in suitablesolvents, such as, for example, aromatic hydrocarbons, such as tolueneor xylene, aromatic halogenated hydrocarbons, such as chlorobenzene,ethers, such as tetrahydrofuran and dioxane, ketones, such as acetoneand cyclohexanone, and/or dimethylformamide, in the presence ofpolymerization initiators which supply free radicals, such as, forexample, azodiisobutyronitrile or benzoyl peroxide, at elevatedtemperatures, as a rule at 30 to 130° C., preferably 40 to 70° C., asfar as possible with exclusion of water and air. They can be isolated byprecipitation with suitable agents, for example methanol. The productscan be purified by reprecipitation, for example withchloroform/methanol.

The polymers according to the invention can form self-supporting films.

Preferably, however, they are applied to carrier materials, for exampleglass or films of plastic. This can be effected by various techniquesknown per se, the process being chosen according to whether a thick orthin layer is desired. Thin layers can be produced, for example, by spincoating or knife coating from solutions or the melt, and thicker layerscan be produced by filling prefabricated cells, melt pressing orextrusion.

The percentage data in the following examples in each case relate to theweight--unless stated otherwise.

EXAMPLES Example 1

A 10⁻³ molar solution of4-(N-methyl-N'-hydroxyethyl)-amino-4'-nitro-azobenzene (molecular weight300) (solution A) and a 1 molar solution of 1,3-dinitrobenzene(molecular weight 168) (solution B) are prepared in dioxane. The1,3-dinitrobenzene must be very pure, and if necessary purified bycrystallization from dioxane. To prepare solution C, 30 mg of thedyestuff are weighed into a 100 ml pipetting flask and topped up withsolution B. Solution C shows a clearly perceptible deepening in colourcompared with solutions A and B. The longwave absorption edges of thethree solutions are recorded with a UV VIS spectrophotometer(Perkin-Elmer, Lambda 3 model) in a 1 cm cell starting from longwavelengths up to the pen buffer. 3 absorption edges which are separatedwell from one another and run essentially parallel are obtained. Thefull deflection of the pen defines the extinction 1.0. The edge ofsolution C reaches the extinction value E_(solution) C =0.8 at λ=575 nm,from which the second readout wavelength of λ+50=625 nm results. Theassociated extinction values are λ=575 nm for E_(solution) A =0.185 andfor E_(solution) B =0.06. At 625 nm, the extinctions are E_(solution) C=0.070, E_(solution) A =0.05 and E_(solution) B =0.025. The extinctiondifferences ΔE_(C) =0.73, ΔE_(A) =0.05 and ΔE_(B) =0.025 result fromthese. From this, it follows that ΔΔE=0.56. The following results arefound for the following compounds by the same method:

    ______________________________________                                          #STR25##                                                                    Ex.    R.sup.1    R.sup.2                                                                             R.sup.3                                                                             R.sup.4   ΔΔE                       ______________________________________                                        2      CH.sub.3   H     H     N(CH.sub.3)C.sub.2 H.sub.4 OH                                                           0.18                                    3 OCH.sub.3 H H N(CH.sub.3)C.sub.2 H.sub.4 OH 0.22                            4 Cl H H N(CH.sub.3)C.sub.2 H.sub.4 OH 0.24                                   5 SO.sub.2 NH.sub.2 H H N(CH.sub.3)C.sub.2 H.sub.4 OH 0.34                    6 CN H H N(CH.sub.3)C.sub.2 H.sub.4 OH 0.40                                   7 CN H CN N(CH.sub.3)C.sub.2 H.sub.4 OH 0.43                                  8 CN CN H N(CH.sub.3)C.sub.2 H.sub.4 OH 0.54                                  9 H H H N(C.sub.2 H.sub.5)C.sub.2 H.sub.4 OH 0.17                             10 OCH.sub.3 H H N(C.sub.2 H.sub.5)C.sub.2 H.sub.4 OH 0.24                    11 Cl H H N(C.sub.2 H.sub.5)C.sub.2 H.sub.4 OH 0.28                           12 CF.sub.3 H H N(C.sub.2 H.sub.5)C.sub.2 H.sub.4 OH 0.39                     13 NO.sub.2 H H N(C.sub.2 H.sub.5)C.sub.2 H.sub.4 OH 0.53                     14 NO.sub.2 H H OCH.sub.3 0.09                                                15 CH.sub.3 H H N(CH.sub.3).sub.2 0.17                                        16 OCH.sub.3 H H N(CH.sub.3).sub.2 0.19                                     ______________________________________                                    

    ______________________________________                                        Ex.      R.sup.1  R.sup.2                                                                             R.sup.3                                                                              R.sup.4                                                                              ΔΔE                         ______________________________________                                        17       H        H     H      N(CH.sub.3).sub.2                                                                    0.21                                      18 Cl H H N(CH.sub.3).sub.2 0.24                                              19 Br H H N(CH.sub.3).sub.2 0.28                                              20 CN H H N(CH.sub.3).sub.2 0.48                                              21 NO.sub.2 H H N(CH.sub.3).sub.2 0.56                                      ______________________________________                                    

Example 22

The dyestuff from Example 1 is reacted with methacryloyl chloride inmethylene chloride in the presence of potash by the process known fromthe literature, the resulting ester is purified by column chromatographyover silica gel and the ΔΔE value of 0.48 is determined by the processdescribed in Example 1.

If the dyestuffs from Examples 4 or 6 are used instead of the dyestufffrom Example 1 and the procedure is otherwise as described above, ΔΔEvalues of 0.27 and 0.47 respectively are obtained.

This thus shows that only group A is important, but it may besubstituted within wide limits and as a result varies the ΔΔE values.

Example 23

If a 1 molar solution of 4cyano-4'-hydroxybiphenyl is used in thedetermination process in Example 1 instead of the 1,3-dinitrobenzenestandard used there, the ΔΔA value is 0.37, and ifN--(4-cyanophenyl)-4-carbamidophenyl-2-oxy-ethylene-methacrylic acidester is employed instead of the 1,3-dinitrobenzene standard, the ΔΔEvalue is 0.47.

This shows that the standard can also be replaced, and in the individualcase can be adapted to the peculiarities of the system.

Example 24

Copolymers of the methacrylic acid esters of the dyestuffs mentioned inExamples 1 to 10 with equimolar amounts of

a) N--(4-cyanophenyl)-4'-carbamidophenyl)-2-oxyethylene-methacrylic acidester and

b) 4-cyano-biphenyl-4'-oxyethylene-methacrylic acid ester

are polymerized in chloroform with AIBN as a free radical initiator.Measurement specimens of the copolymers are produced on glass plates 2×2cm in size and of thickness 1.1 mm by placing them in a spin coater(model Suss RC 5) and coating them with 0.2 ml of a solution of 150 g ofthe polymers shown below in 1 liter of absolute tetrahydrofuran at 2000rpm in the course of 10 seconds. The layer is 0.9 μ thick, transparentand amorphous. Between crossed polarizers, the surface appears uniformlydark. No signs of polarizing regions are observed.

The measurement plates are exposed to light from an Ar ion laser with anoutput of 60 mW at a wavelength of 514 nm, a birefringence building up,which is measured. The results obtained are:

    ______________________________________                                        Dyestuff           Δn                                                   example  ΔΔE                                                                         Copolymer 24a                                                                            Copolymer 24b                                   ______________________________________                                        10       0.17                 0.011                                             2 0.18 0.021                                                                  3 0.22 0.089 0.079                                                            4 0.24  0.019                                                                 6 0.40 0.063 0.074                                                            7 0.43 0.038 0.077                                                            8 0.54 0.024                                                                  1 0.56 0.074 0.116                                                          ______________________________________                                    

The example shows that the ΔΔE value correctly predicts therepresentatives with a high change in birefringence independently of thechoice of the group M.

What is claimed is:
 1. A polymer having a main chain as a backbone and,branching therefrom, covalently bonded side groups of the formulae

    --S.sup.1 --T.sup.1 --Q.sup.1 --A                          (I) and

    --S.sup.2 --T.sup.2 --Q.sup.2 --M                          (II)

wherein S¹ and S² denote the atoms O or S or the radical NR⁰, or COO R⁰denotes hydrogen or C₁ -C₄ -alkyl, T¹ and T² denote the radical(CH₂)_(n), which can optionally be interrupted by --O--, --NR⁰ -- or--OSiR⁰ ₂ O-- and/or can optionally be substituted by methyl or ethyl,Q¹ and Q² denote a direct single bond, --O--, --COO--, --OCO--, --CONR⁰,--NR⁻ CO⁰ -- or --NR⁰ --, or S¹ T¹ Q¹ or S² T² Q² denotes a bivalentgroup of the formula ##STR26## A denotes a unit which can absorbelectromagnetic radiation, M denotes a mesogenic unit anisotropic inshape and n denotes an integer from 2 to 12, wherein A has an extinctionmodulus ΔΔE of greater than 0.2, measured on a compound of the formulaA--Q¹ H or AQ¹ T¹ S¹ H by 6 individual measurements:A) A--Q¹ H or AQ¹ T¹S¹ H in the lowest possible concentration in a solvent of the lowestpossible polarity, B) standard in the highest possible concentration inthe same solvent, C) A--Q¹ H or AQ¹ T¹ S¹ H and standard in theconcentration as above in the same solventmeasured in each case twice atthe longer-wavelength edge of the absorption curve, and measured once ata wavelength λ at which the extinction of curve C is 0.8, and once at awavelength λ+50 nm, the three differences of the extinctionΔE═E.sub.λ+50 being obtained for the ingredients A) to C), and the threevalues ΔE_(A) and ΔE_(B) and ΔE_(C) being obtained, the value ΔΔE soughtthen being the difference ΔΔE=ΔE_(C) -(ΔE_(B) +ΔE_(A)), and with theproviso that the polymer does not include group A having the formula:##STR27## wherein R¹⁴ to R¹⁶ independently of one another denote C₁ -C₆-alkyl, hydroxyl, C₁ -C₆ -alkoxy, phenoxy, C₁ -C₆ -alkylthio,phenylthio, halogen, CF₃, CCl₃, CBr₃, nitro, cyano, C₁ -C₆-alkylsulphonyl, phenylsulphonyl, COOR¹, aminosulphonyl, C₁ -C₆-alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C₁ -C₆-alkylaminocarbonyl or phenylaminocarbonyl, R¹⁷ denotes halogen, C₁ -C₆-alkyl, hydroxyl, C₁ -C₆ -alkoxyl, phenoxy, C₁ -C₄ -acylamino or C₁ -C₄-alkylsulphonylamino, R¹⁸ denotes halogen, C₁ -C₆ -alkyl, hydroxyl, C₁-C₆ -alkoxy or phenoxy and X¹ denotes hydrogen, hydroxyl, mercapto, CF₃,CCl₃, CBr₃, halogen, cyano, nitro, COOR¹⁹, C₁ -C₆ -alkyl, C₅ -C₁₂-cycloalkyl, C₁ -C₁₂ -alkoxy, C₁ -C₁₂ -alkylthio, C₆ -C₁₂ -aryl, C₆ -C₁₂-aryloxy, C₆ -C₁₂ -arylthio, C₁ -C₆ -alkylsulphonyl, C₆ -C₁₂-arylsulphonyl, aminosulphonyl, C₁ -C₆ -alkylaminosulphonyl,phenylaminosulphonyl, aminocarbonyl, C₁ -C₆ -alkylaminocarbonyl,phenylaminocarbonyl, NR¹⁹ R²⁰, NH-CO-R¹⁹, NH-SO₂ -R¹⁹, NH-CO-NR-¹⁹ R²⁰,NH-CO-O-R¹⁹ or SO₂ -CF3, wherein R¹⁹ and R²⁰ independently of oneanother represent hydrogen, C₁ -C₄ -alkyl or phenyl.
 2. A polymer havinga main chain as a backbone and, branching therefrom, covalently bondedside groups of the formulae

    --S.sup.1 --T.sup.1 --Q.sup.1 --A                          (I) and

    --S.sup.2 --T.sup.2 --Q.sup.2 --M                          (II)

wherein S¹ and S² denote the atoms O or S or the radical NR⁰, or COO R⁰denotes hydrogen or C₁ -C₄ -alkyl, T¹ and T² denote the radical(CH₂)_(n), which can optionally be interrupted by --O--, --NR⁰ -- or--OSiR⁰ ₂ O-- and/or can optionally be substituted by methyl or ethyl,Q¹ and Q² denote a direct single bond, --O--, --COO--, --OCO--, --CONR⁰,--NR⁻ CO⁰ -- or --NR⁰ --, or S¹ T¹ Q¹ or S² T² Q² denotes a bivalentgroup of the formula ##STR28## A denotes a unit which can absorbelectromagnetic radiation, M denotes a mesogenic unit anisotropic inshape and n denotes an integer from 2 to 12, wherein A has an extinctionmodulus ΔΔE of greater than 0.2, measured on a compound of the formulaA--Q¹ H or AQ¹ T¹ S¹ H by 6 individual measurements:A) A--Q¹ H or AQ¹ T¹S¹ H in the lowest possible concentration in a solvent of the lowestpossible polarity, B) standard in the highest possible concentration inthe same solvent, C) A--Q¹ H or AQ¹ T¹ S¹ H and standard in theconcentration as above in the same solvent measured in each case twiceat the longer-wavelength edge of the absorption curve, and measured onceat a wavelength λ at which the extinction of curve C is 0.8, and once ata wavelength λ+50 nm, the three differences of the extinctionΔE═E.sub.λ+50, being obtained for the ingredients A) to C), and thethree values ΔE_(A) and ΔE_(B) and ΔE_(C) being obtained, the value ΔΔEsought then being the difference ΔΔE=ΔE_(C) -(ΔE_(B) +ΔE_(A)), with theproviso that said group A does not include an unsubstituted ##STR29##and with the further proviso that the ploymer does not include group Ahaving the formula: ##STR30## wherein R¹⁴ to R¹⁶ independently of oneanother denote C₁ -C₆ -alkyl, hydroxyl, C₁ -C₆ -alkoxy, phenoxy, C₁ -C₆-alkylthio, phenylthio, halogen, CF₃, CCl₃, CBr₃, nitro, cyano, C₁ -C₆-alkylsulphonyl, phenylsulphonyl, COOR¹, aminosulphonyl, C₁ -C₆ -alkylaminosulphonyl, phenylaminosulphonyl, aminocarbonyl, C₁ -C₆-alkylaminocarbonyl or phenylaminocarbonyl, R¹⁷ denotes halogen, C₁ -C₆-alkyl, hydroxyl, C₁ -C₆ -alkoxy, phenoxy, C₁ -C₄ -acylamino or C₁ -C₄-alkylsulphonylamino, R¹⁸ denotes halogen, C₁ -C₆ -alkyl, hydroxyl, C₁-C₆ -alkoxy or phenoxy and X¹ denotes hydrogen, hydroxyl, mercapto, CF₃,CCl₃, CBr₃, halogen, cyano, nitro, COOR¹⁹, C₁ -C₆ -alkyl, C₅ -C₁₂-cycloalkyl, C₁ -C₁₂ -alkoxy, C₁ -C₁₂ -alkylthio, C₆ -C₁₂ -aryl, C₆ -C₁₂-aryloxy, C₆ -C₁₂ -arylthio, C₁ -C₆ -alkylsulphonyl, C₆ -C₁₂-arylsulphonyl, aminosulphonyl, C₁ -C₆ -alkylaminosulphonyl,phenylaminosulphonyl, aminocarbonyl, C₁ -C₆ -alkylaminocarbonyl,phenylaminocarbonyl, NR¹⁹ R²⁰, NH-CO-R¹⁹, NH-SO₂ -R¹⁹, NH-CO-NR¹⁹ R²⁰,NH-CO-O-R¹⁹ or SO₂ -CF3, wherein R¹⁹ and R²⁰ independently of oneanother represent hydrogen, C₁ -C₄ alkyl or phenyl.